maui-linux/Xamarin.Forms.Platform.GTK/Cells/ViewCell.cs

using System;
using static Xamarin.Forms.Platform.GTK.Platform;

namespace Xamarin.Forms.Platform.GTK.Cells
{
    internal class ViewCell : CellBase
    {
        private WeakReference<IVisualElementRenderer> _rendererRef;
        private Gdk.Rectangle _lastAllocation;

        protected override void OnSizeAllocated(Gdk.Rectangle allocation)
        {
            base.OnSizeAllocated(allocation);

            if (_lastAllocation != allocation)
            {
                _lastAllocation = allocation;

                var viewCell = Cell as Xamarin.Forms.ViewCell;
                var view = viewCell.View;

                if (view == null)
                {
                    return;
                }

                double width = allocation.Width;
                double height = DesiredHeight > 0
                                ? DesiredHeight
                                : Cell.RenderHeight > 0
                                    ? Cell.RenderHeight
                                    : GetHeightMeasure(viewCell, allocation);

                Layout.LayoutChildIntoBoundingRegion(view, new Rectangle(0, 0, width, height));

                if (_rendererRef == null)
                    return;

                IVisualElementRenderer renderer;
                if (_rendererRef.TryGetTarget(out renderer))
                {
                    renderer.Container.WidthRequest = (int)width;
                }
            }
        }

        private double GetHeightMeasure(Xamarin.Forms.ViewCell viewCell, Gdk.Rectangle allocation)
        {
            var request = viewCell.View.Measure(allocation.Width, double.PositiveInfinity, MeasureFlags.IncludeMargins);

            return request.Request.Height;
        }

        public override void Dispose()
        {
            IVisualElementRenderer renderer;
            if (_rendererRef != null && _rendererRef.TryGetTarget(out renderer) && renderer.Element != null)
            {
                _rendererRef = null;
            }

            base.Dispose();
        }

        protected override void UpdateCell()
        {
            var viewCell = Cell as Xamarin.Forms.ViewCell;

            if (viewCell != null)
                Device.BeginInvokeOnMainThread(viewCell.SendDisappearing);

            Device.BeginInvokeOnMainThread(viewCell.SendAppearing);

            IVisualElementRenderer renderer;
            if (_rendererRef == null || !_rendererRef.TryGetTarget(out renderer))
                renderer = GetNewRenderer();
            else
            {
                if (renderer.Element != null && renderer == Platform.GetRenderer(renderer.Element))
                    renderer.Element.ClearValue(Platform.RendererProperty);

                var type = Internals.Registrar.Registered.GetHandlerType(viewCell.View.GetType());
                if (renderer.GetType() == type || (renderer is DefaultRenderer && type == null))
                    renderer.SetElement(viewCell.View);
                else
                {
                    renderer = GetNewRenderer();
                }
            }

            Platform.SetRenderer(viewCell.View, renderer);
        }

        private IVisualElementRenderer GetNewRenderer()
        {
            var viewCell = Cell as Xamarin.Forms.ViewCell;

            if (viewCell.View == null)
            {
                return null;
            }

            var newRenderer = Platform.CreateRenderer(viewCell.View);

            _rendererRef = new WeakReference<IVisualElementRenderer>(newRenderer);
            Add(newRenderer.Container);

            return newRenderer;
        }
    }
}